1. Field of the Invention
The present invention relates to a power transmission device of an engine and, more particularly to a power transmission device of an engine having a mechanism for changing a rotational direction of output of the engine by substantially 90 degrees.
2. Description of the Related Art
There are various types of engines according to uses. For example, an engine includes a drive shaft extending in a direction orthogonal to a crank shaft of the engine. Such an engine is adopted as an engine of a shaft drive type motor cycle, an engine of a straddle-type four wheel all terrain vehicle, or the like.
FIG. 5 is a cross-sectional view showing a portion of an engine of a straddle-type four wheel all terrain vehicle, including a drive shaft 121 and its vicinity. In this engine, a gear-type transmission unit is accommodated in a gear case portion 131 integrated with a crank case. A counter shaft 142 of the gear-type transmission unit is shown in FIG. 5. A spur gear 143 is attached to the counter shaft 142 for transmitting power from an input shaft (not shown) of the gear-type transmission unit to an output shaft 111 of the gear-type transmission unit. The output shaft 111 of the gear-type transmission unit is rotatably supported by the gear case portion 131 of the crank case via a bearing 114. A spur gear 116 is fixed to the output shaft 111 for driving the output shaft 111. The spur gear 116 is in mesh with the spur gear 143 of the counter shaft 142. Thereby, a rotational driving force of the spur gear 143 is transmitted to the output shaft 111.
A gear case 132 is removably attached to the gear case portion 131 of the crank case. The gear case portion 131 and the gear case 132 are separate portions. A driving bevel gear 112 is attached to a tip end portion of the output shaft 111. The tip end portion of the output shaft 111, together with the driving bevel gear 112, protrudes from the gear case portion 131 of the crank case and is accommodated in the gear case 132. A drive shaft 121 is rotatably supported by the gear case 132. A driven bevel gear 122 provided on the drive shaft 121 is accommodated in the gear case 132.
More specifically, the driven bevel gear 122 is fixed to the drive shaft 121. The drive shaft 121 is rotatably supported by a support member 123 via a bearing 124. The support member 123 is attached to the gear case 132. A portion of the drive shaft 121, including the driven bevel gear 122, is accommodated in the gear case 132. Since the driven bevel gear 122 is in mesh with the driving bevel gear 112, a direction of a rotational driving force of the output shaft 111 is changed by 90 degrees and the resulting force is transmitted to the drive shaft 121 in the gear case 132.
An adjustment shim 115 is attached on a rear face of the driving bevel gear 112. The adjustment shim. 115 enables adjustment of an axial position of the driving bevel gear 112 with respect to the output shaft 111. An adjustment shim 125i, is interposed between the gear case 132 and the support member 123. These shims 115, 125 serve to adjust tooth contact between the driving bevel gear 112 and the driven bevel gear 122. The shims 115, 125 are changed among shims having various thicknesses to select the shims 115, 125 having thicknesses for preferable tooth contact between the driving bevel gear 112 and the driven bevel gear 122.
However, the power transmission device of the engine described above have the following problems.
(1) Since the gear case 132 as the part separable from the crank case is placed laterally of the crank case, a lateral width of the engine and weight of the engine are increased. In addition, since the gear case 132, i.e., a member different from the crank case is necessary, the number of parts of the engine and a manufacturing cost thereof are increased.
(2) When the shim 115 is changed or checked after the gear case 132 into which the drive shaft 121 has been assembled is attached to the gear case portion 131 of the crank case, a burdensome operation, i.e., removal of the gear case 132 including the drive shaft 121 from the crank case, becomes necessary. In particular, in a case where an engine has been assembled into a vehicle, the removal of the gear case 132 from the crank case is very burdensome.
As an example of a structure of a compact engine, it is known that a drive shaft is provided in a gear case portion of a crank case and a driven bevel gear of the drive shaft is accommodated in the gear case portion of the crank case. In this case, the tooth contact adjustment between the bevel gears is not necessarily easy, including the need for disassembly of the crank case, and its structure is complex. Such a related art is disclosed in Japanese Laid Open Patent Publication No. Sho. 63-71424, Japanese Laid Open Patent Publication No. Sho. 61-63828.
The present invention has been developed for obviating the above-described problems and an object of the present invention is to provide a power transmission device of an engine, which is lightweight, has few parts, and realizes a reduced width of the engine and easy adjustment of tooth contact between bevel gears when applied to the engine.
To solve the above-described problems, there is provided a power transmission device of an engine comprising: an output shaft of a gear-type transmission unit which is provided in parallel with a crank shaft of the engine and provided with a driving bevel gear at one end thereof, a driving force from the crank shaft being transmitted to the output shaft; a drive shaft placed in a direction orthogonal to the output shaft and provided with a driven bevel gear which meshes with the driving bevel gear; a gear case formed integrally with a crank case for accommodating the gear-type transmission unit and supporting a shaft situated in a previous stage of the output shaft at both ends of the shaft; a lid member; a first support member; a first shim; a second support member; and a second shim; wherein an opening is formed in the gear case to allow the output shaft to be pulled out of the gear case in a direction from the one end of the output shaft toward the other end thereof, the lid member is removably attached to the gear case such that it closes the opening, the first support member is removably attached to the gear case for rotatably supporting the output shaft, the first shim is interposed between the first support member and the gear case, the second support member is removably attached to the gear case for rotatably supporting the drive shaft, and the second shim is interposed between the second support member and the gear case.
Since the gear case and the crank case are integrally formed as described above, the engine can be made compact and the number of parts of the engine can be reduced. In particular, a width of the engine can be reduced. Besides, the first support member supporting the output shaft, and hence the first shim, can be taken out of the gear case through the opening by detaching the lid member from the gear case. Consequently, change and check of the first shim becomes easy. To form the gear case integrally with the crank case, for example, the crank case including the gear case as a portion of crank case may be manufactured by molding aluminum alloy.
It is preferable that in the power transmission device of the engine, the engine comprises a belt-type transmission unit for transmitting the driving force of the crank shaft to the gear-type transmission unit, and the drive shaft is situated in the gear case between the belt-type transmission unit provided in a side portion of the crank case and the gear-type transmission unit provided in the gear case. With such a structure, a dimension of the engine in a width direction thereof can be reduced.
It is preferable that in the power transmission device of the engine, the first support member supports the output shaft at a central portion thereof to prevent the output shaft from moving in an axial direction thereof, the output shaft is provided with the driving bevel gear in the gear case, which is situated closer to the belt-type transmission unit than the first support member, the output shaft is provided with a gear for driving the output shaft in the gear case, which is situated farther from the belt-type transmission unit than the first support member, the gear case has the opening formed laterally of the gear for driving the output shaft, and the opening is sufficiently large to allow the gear for driving the output shaft and the first support member to pass therethrough. With such a structure, shim adjustment in the axial direction of the output shaft becomes especially easy.
It is preferable that in the power transmission device of the engine, the gear case includes a support boss having a support hole inside thereof, the first support member includes a shaft portion for supporting the output shaft via a bearing and a flange portion having a flange face facing toward an axial direction of the output shaft, the shaft portion of the first support member is inserted into the support hole, and an end face of the support boss and the flange face of the first support member are connected via the first shim to allow an axial position of the output shaft with respect to the gear case to be regulated.
It is preferable that in the power transmission device of the engine, the second support member supports the drive shaft to prevent the drive shaft from moving in an axial direction thereof, a fitting hole is formed in a wall portion of the gear case which has a wall face substantially orthogonal to the drive shaft such that the fitting hole is sufficiently large to allow the driven bevel gear to pass therethrough, and the second support member is removably fitted to the fitting hole. With such a structure, shim adjustment in the axial direction of the drive shaft becomes especially easy.
It is preferable that in the power transmission device of the engine, the second support member includes a shaft portion and a flange portion having a flange face facing toward an axial direction of the drive shaft, a fitting face is formed in the vicinity of the fitting hole in an outer wall face of the gear case such that the fitting face is opposed to the flange face of the second support member, the shaft portion of the second support member is fitted into the fitting hole, and the fitting face and the flange face of the second support member are connected via the second shim to allow an axial position of the drive shaft with respect to the gear case to be regulated.
These objects as well as other objects, features and advantages of the invention will become apparent to those skilled in the art from the following description with reference to the accompanying drawings.